A data center could achieve disk utilization rates of 99 percent and a PUE of 1.2, but if that same datacenter is failing to de-duplicate data, it's probably wasting storage space and energy, he notes.
"I absolutely love PUE," Peters says. "But datacenter efficiency is a much bigger topic than power usage efficiency."
Two years after being proposed, PUE is starting to catch on. Officials at the SuperNAP co-location center in Las Vegas use internal PUE measurements to argue that the data center is the most energy efficient in the world. PUE is being adopted by the European Union within its datacenter code of conduct standard, according to Green Grid officials. But PUE should still be seen as an interim metric, says Mark Monroe of the Green Grid's board of directors.
"What everyone wants to get to is what are the computers doing with that electricity, and how efficient is that computer?" says Monroe, who is also the director of sustainable computing at Sun. "How much useful work is coming out of that computer?"
Today, there's little sense in comparing one datacenter to another because companies might be measuring it differently, Monroe says. PUE is mainly useful as an internal metric to compare your data center to itself over time, he says. The Green Grid's Web site details what must be measured to calculate PUE, such as power delivery components like UPS, switching gear, generators, power distribution units, batteries, and power losses. But the organization is still working toward implementing detailed specifications and a certification program in which it will verify PUE at individual facilities. That should happen within a year, Green Grid officials say.
Gaining enterprise attention
While PUE has gained traction among industry powers such as Google and Microsoft, which both boast of low PUE ratings, Peters says enterprise customers for the most part aren't measuring it at their own data centers.
"It's too new for it to have filtered that far," he says.
Still, numerous vendors have stepped up to provide software tools for measuring both total IT power usage and the power devoted to individual devices. And some large enterprises have begun tracking PUE and how it changes over time.
James Carney, executive vice president of datacenter planning at Citigroup in New York, says he measures PUE at all the company's datacenters, but getting a meaningful measurement is difficult at facilities that include both data center equipment and office space.
"The only places you can very accurately measure it are where you have stand-alone, purpose-built datacenters," Carney says. In one such datacenter in Texas, Carney says Citi has achieved average PUE ratings of 1.58 to 1.62.
The keys for Carney include partnering with the company's real estate organization, using energy management software and control systems that track power entering all points of the datacenter, and using all the data to optimize cooling temperatures.
"People look at watts per square foot. They look at chilled water temperature. PUE gives a pretty holistic view of what's going on in the entire environment," Carney says. "We also like to measure [power usage] at the cabinet level and different areas of the datacenter floor."